Facsimile (FAX) machines have long been used as a convenient system for transmitting data from one location to another. A transmitting FAX machine transmits a facsimile message over a telephone line to a receiving FAX machine. The telephone line may be a wire or optical cable, or may include a remote connection such as a microwave or satellite link. Thus, a user may send the facsimile message from one FAX machine to another FAX machine located anywhere in the world via the telephone line.
The cost of sending a facsimile message long distance includes the transmission cost of the telephone call which is directly related to the length of the message being sent and the time at which the facsimile telephone call is placed. To reduce costs, the user may send the facsimile message during low-cost periods, such as at night, when the demand for telephone lines is minimal. Thus, the phone rate is decreased and the cost of sending the facsimile message is correspondingly decreased.
The cost can also be reduced by minimizing the duration of the facsimile telephone call. One such method for minimizing the duration is to compress the data prior to transmission. Early facsimile machines used a basic data encoding technique, known as Modified Huffman (MH) encoding. This form of encoding permits compression of the facsimile message, with a corresponding decrease in the duration of the facsimile telephone call. Other data encoding techniques were developed for newer facsimile machines, although newer facsimile machines continue to retain MH encoding capability to enable facsimile communication with machines of the older design. A Modified Read (MR) encoding permits two-dimensional data encoding, which permits a higher degree of data compression than MH encoding. Both MH and MR encodings are described in standards established by the International Telegraph and Telephone Consultative Committee (CCITT) and published as Terminal Equipment and Protocols for Telematic Services (1989). The MH and MR data encodings are described in recommendation T.4 of the CCITT standard.
A third type of data compression is the Modified Modified Read (MMR encoding), which is described in recommendation T.6 of the CCITT standard and permits two-dimensional encoding of low- or high-resolution facsimile messages.
The techniques used for encoding a facsimile message using MH, MR, or MMR are described in the CCITT standard. References to the CCITT standards are made throughout this disclosure. The standards and the techniques used for MH, MR and MMR data encodings are well known to those skilled in the art and will not be discussed in detail.
When a facsimile telephone call is first initiated, the transmitting FAX machine does not know what data encoding capabilities the receiving FAX machine may have. Because of this, the facsimile message is not encoded using one of the above encoding techniques until after the facsimile telephone call is initiated and the data encoding capabilities of the receiving FAX machine are made known to the transmitting FAX machine. Encoding and hence transmission of the facsimile message does not occur until after the receiving FAX machine sends a digital identification signal (DIS) to the transmitting FAX machine. The DIS contains information indicating the data encoding capabilities of the receiving FAX machine. The transmitting FAX machine uses the information in the DIS to determine the appropriate data encoding format. As a result, the facsimile message is encoded during the facsimile telephone call.
A drawback of the data encoding algorithms described in the CCITT standard is that they are slow and require a longer duration facsimile telephone call. Therefore, it can be appreciated that there is a significant need for a system and method to improve facsimile data encoding and reduce facsimile transmission costs.